The earthquake is defined as shaking of crust of earth by spreading of vibrations in the form of wave due to breaks in the earth's crust. Earthquake, a natural phenomenon indicates that earth can also move and all the buildings on it can be harmed and people could die.
The science engaged with how earthquakes occur, spreading of earthquake wave on the earth crust, measuring instruments and methods, evaluation and registrations and readings and other issues related to the earthquake is called “SEISMOLOGY”
There is an earth model supported by data obtained from geological and geophysical studies about the internal structure of the earth. According to this model there is lithosphere at the Earth's outer part of 70-100 km thickness. Continents and oceans are located in this lithosphere. There is mantle between the core and lithosphere with thickness of 2,900 km. The bottom of the mantle is considered to consist of a mixture of nickel-iron core. It is known that temperature increases from surface to deeper. It is estimated to be average 5000-6000° C. It is concluded that core has a liquid structure depending on the fact that transverse seismic waves don't spread towards core of earth.
In general mantle is solid at surface, towards core there are local liquid layers.
There is soft upper mantle under earth crust which is called asthenosphere.
The forces formed here, especially the stone crust due to convection currents, are fragmented and divided into many “Plates”. Convection currents formed on the upper mantle are connected to temperatures caused by radioactivity.
As convection currents increase, it cause stress on stone rollers and then leads to the formation of plates by breaking weak zones. Already there are ten big plates and many small plates. These plates float on asthenosphere with continents like a boat and move relative to each other with a speed not perceived by people.
In places where the convection currents rise, the pates move away from each other and form the oceanic ridge in the hot magma coming out of them. At locations where plates come into contact with each other friction and compression occurs. One of the friction plates sink into the mantle below and constitute subduction zones by melting. These sequential events caused by convection currents continue under crust of earth.
Boundaries of these plates which rub each other, compress each other, climb each other or fall under each other appear as earthquake in the world. Vast majority of earthquakes occurring in the world take place on narrow zones at plate boundaries where they force each other.
There is a frictional force between two plates pushing each other or entering under each other that prevents motion. For the motion of such a plate this friction force must be overcome.
When the friction force between one pushed plate and another plate is exceeded a movement takes place. This action takes place in a very short time and has a form of shock. Finally, earthquake waves which can spread very far (shock) occur. These waves shake the environment as they pass through and energy decreases as waves get farther from the direction of earthquake. Meanwhile land fractures occur on earth which is called as fault line and sometimes visible and extend for miles. These fractures are sometimes not observable on earth and they might be hidden by the surface layers. Sometimes, an old fault line formed due to an old earthquake but covered in time can move again.
In this way formation of the earthquake was described under the theory of “elastic rebound theory” by American Reid in 1911 and has been proven in laboratory with experiments.
According to this theory, energy preserved by unit deformation accumulation elastically depending on time at any point reaches a critical value, it defeats the friction that exists along the fault line and cause motion of fault lines on both sides of rock forms relative to each other. This event is the sudden displacement movement.
This sudden displacement occurs due to discharge of unit deformation energy accumulated at a specific point, discharge in other words with the conversion to mechanical energy, and as a result due to breaking and tearing of earth layers.
In fact, it is impossible for rocks to break without the accumulation of a pre-displacement unit. These unit displacement movements are created by convection currents that occur in the upper mantle, and rocks may show strength until a certain deformation and then get fractured. These breakage results in earthquakes. After such cases a part of stress and energy accumulated away from the rocks are removed.
Mostly on faults occurring during this earthquake, elastic re-bounds (stroke) are formed on both sides of the faults in the opposite direction.
Faults are usually named according to the direction of movement. Faults with more horizontal movement results in “strike-slip faults.” In addition, two separate blocks that form the fault may have movement relative to each other from left or right which is an example of the right or left lateral strike-slip faults.
Faults occurring due to vertical movement are called “dip-slip faults”. Most of the faults may have both horizontal and vertical movements.
Earthquakes are natural events, each hosting its own unique and many unpredictable variables. Considering the many possibilities, earthquake should be treated according to its structure. Studies for the calculation of the behavior of your structure and the strength during major earthquake is the ideal for mankind. For the sake of this many laws, regulations, calculations and specifications were made and continues.
In general, in all the calculations and studies made in the world, only effects of horizontal direction of earthquakes are taken into account. Engineers calculate earthquake loads to effect structure from both sides similarly and distribute these loads to structure floors at specific rates. In buildings constructed by considering only horizontal forces ductility of nonlinear beams and curtains cannot be calculated correctly. This situation mostly results in bending on collapse of these structures. Probability of survival of people within this type of structure is very less.
Today, rubber isolators and pendulum isolators are used to protect structure against earthquakes. Rubber isolators are formed with rounded rubbers placed between steel plates. Here, it is believed that earthquake is isolated due to rubber horizontal shift and horizontal displacement of each of 15-20 plates. Rubber isolators should be placed between the columns and beams in single-story structures with or between foundation and structure (viaduct, bridge, and hangar). Rubber isolators disconnect link between foundation and structure. It is not possible for structure to transfer momentum to foundation. Horizontal forces are also suspected to be transferred to foundation. If rubber isolators make horizontal displacement between each plate, it allows vertical displacement as well. In this case because building will try to be overthrown during earthquake due to the centrifugal force, when building is disconnected from foundation building will overturn. This system cannot be applied in the multi-story buildings. The risks posed to rubber during the fire, should be taken into account.
Pendulum isolators consist of two parts. There is no connection with the basic structure as in the rubber isolator. It cannot handle the momentum of the building and because adherence will increase due to weight of building, shift of the pendulum isolators will be weaken. This situation is a barrier to achieve the desired result. It is not suitable for multi-story buildings. It can cause the collapse of a structure and the earthquake can heavily damage the structure.